The present invention relates to binders, more specifically, starch based binders for non-woven fibers such as polyester, polypropylene, fiberglass or cellulosic fibers.
Fibers, such as polyester fibers are often dry-laid to form a mat which is then fed through a pad bath to apply a binder which is then dried and cured. For roofing the binder-treated polyester mat is fed through a hot asphalt bath to apply a coating of asphalt. Due to the high temperature of the asphalt bath, polyester mats often stretch, resulting in a great decrease in the width of the mat.
Binders are known which reduce shrinkage of the mat width. Conventional binders comprise an acrylic or a vinyl-acrylic latex emulsion. For example, U.S. Pat. No. 4,617,229 describes a latex-type binder which is a mixture of methyl methacrylate and ethylacrylate and which is used to bind non-woven fabric for the carcass of a water-proofing membrane used in roofing.
Non-woven fabrics cover a wide array of products including consumer goods like mattress dust shields, disposable diaper cover fabrics, cleaning towels, carpets, draperies and industrial and commercial goods like wipe cloths, tire cords, conveyor belts, hospital fabrics, etc. The technology for non-woven production includes filament or staple filters processed through a dry or wet-lay sheet formation step and bonded by thermal, mechanical or chemical means. Laminations of non-wovens to other non-wovens, film sheets or traditional woven or knitted textiles are often still classified as non-wovens.
One of the non-woven bonding methods is to treat a staple or filament fiber sheet with an emulsion polymer containing a formaldehyde based crosslinking resin in order to impart water and solvent resistance When the emulsion is dried and cured the polymer forms intimate bonding of the fibers This polymer deposition modifies the strength, stiffness, environmental resistance, elongation and many other characteristics of the fiber fabric sheet. The fiber can be from a great variety of compositions, e.g. rayon, wood pulp (cellulose), cotton, nylon, polyester, glass and graphite In the case of carded staple fiber the polymer usually contributes most of the strength and toughness character in the resulting non-woven. In wet-laid wood pulp fiber products the polymer is able to provide the non-woven strength and resistance to aqueous and solvent environments which the untreated non-woven would not have. In glass mat non-wovens traditionally bonded with a urea-formaldehyde resin, addition of emulsion polymers alters the toughness of the resulting non-woven. Even in filament or staple fiber non-wovens which are bonded by mechanical (i.e. needle punching) or thermal (e.g. spun bonded) techniques and are formed into useful non-woven fabrics without a chemical treatment, an additional application of an emulsion polymer can enhance or produce other valuable characteristics such as stretch resistance or non-slip character.
Melamine-formaldehyde resins do not build viscosity in the binder until cured, but they have the disadvantage of having an unpleasant odor and of releasing free formaldehyde. Curing with such resins involves the crosslinking of binder molecule with the methylol or methylated methylol group of the melamine resin. Free formaldehyde can be released either directly from the binder or mixture or when the coating is cured on the drying machine. The presence of even less than one percent of free formaldehyde, based on the total weight of the product, is undesirable, not only because of its objectionable odor, but because it is an allergen and an irritant, causing severe reactions in the operators who manufacture the binders and who treat and handle the non-woven fibers or fabrics.